I. Field of the Present Invention
The present invention relates generally to torque transfer apparatus, and more particularly to an axle drive which delivers torque from a drive line to the wheels of a motor vehicle.
II. Description of the Prior Art
Typically, a vehicle engine is coupled through a transmission to a single drive ine in a two-wheel drive vehicle i.e. having a single driven axle set, while a transfer case having a drive line extending toward each axle is coupled to the transmission in a four-wheel drive vehicle, i.e. having two driven axle sets. An axle drive operatively connects the torque delivered through each drive line to the axle shafts which rotatably drive the wheels of an axle set.
In a typical axle drive mechanism, an input shaft is rotatably supported in a longitudinal extension of a main housing which contains an axle shaft for each wheel and gear means for coupling the input shaft to the axle shaft. The longitudinal extension is required because the longitudinal axis of the input shaft is perpendicular to the longitudinal axis of the axle shafts but within the same horizontal plane. A pinion gear is mounted on one end of the input shaft and positively engages a driven gear of the gear means which is coaxially mounted about an axle shaft. The axle drive gear means often comprises differential gear means so that the torque from the input shaft is split between the two axially aligned axle shafts as necessary to provide interwheel differential action in a well known manner.
In order to rotatably support the pinion gear in a stable position for positive engagement with the driven gear, the extended portion of the axle drive housing often includes a pair of axially spaced bearings. The spaced apart bearing arrangement avoids misalignment of the longitudinal axis of the shaft due to gear tooth load which can interfere with proper meshing engagement between the pinion and driven gears. Moreover, while mounting of the pinion gear at the end of the input shaft permits the axial end of the input shaft to be spaced radially away from the axle shafts so that neither of the shafts obstructs the other, the extended housing portion substantially increases the longitudinal dimension of the drive housing. In addition, the input shaft is accessible only from one end of the drive axle housing.
While the elongated housing portion containing the input shaft can be easily accommodated in a rear wheel drive vehicle having a front engine mounting by merely using a shorter drive shaft between the transmission and the axle housing, the length of the axle drive housing can be especially disadvantageous in front wheel drive vehicles and four-wheel drive vehicles. In particular, since the vehicle engine, transmission, suspension components and steering components are often housed in the forward part of the vehicle chassis, there is a limited amount of space available which can be occupied by the drive axle. Consequently, it would be advantageous to make each component as compact as possible so as to avoid increasing the overall size and weight of the vehicle.
In addition, while it is advantageous to provide an even distribution of vehicle weight upon the axles, one axle often carries a greater load than the other. Consequently, when the wheels of two axle sets are driven, the axle drive for each axle set must be capable of handling a proportion of torque corresponding to the load distributed to its axle set. While it may be possible to downsize an axle drive which receives only a portion of the torque on a part time basis, downsizing is not practical for an axle drive subjected to full torque or used as the primary drive axle. However, while reducing the length of the extended housing portion of the axle drive mechanism might be possible by spacing the bearings closer together or eliminating one of the bearing sets used to support the input shaft, such modifications result in a less stable alignment of the input shaft. As a result, the bearings, the gears and other components of the axle drive become subjected to additional stresses which increases the wear on the parts. Consequently, the parts have a shorter life and induce greater heat buildup which can induce deterioration of the parts and the lubricants enclosed within the housing.
Moreover, since the chassis structure at the front of the vehicle may differ substantially from the chassis construction at the rear of the vehicle, the front axle drive mechanism is often differently constructed from the drive mechanism used at the rear of the vehicle, and the two axle drive mechanisms are not interchangeable. Thus, a substantial amount of expense is incurred in designing, manufacturing and assembling the various constructions of axle drives which are currently available. Moreover, substantial duplication of function with non-interchangeable drive axle components substantially increases the initial cost of the vehicle as well as the cost of repairing it.
Moreover, one previously known axle drive mechanism having inputs at both ends of the axle drive housing is disclosed in U.S. Pat. No. 4,511,012 to Rauneker. Rauneker discloses an axle drive mechanism constructed in the previously known manner having an input shaft rotatably supported within a longitudinally extended housing portion with a pinion gear mounted at one end in engagement with a driven gear of a differential gear unit. The axle drive mechanism also includes an additional input shaft spaced radially apart from and substantially parallel to the first input shaft. The second input extends outwardly from the other end of the housing. A gear mechanism interconnects the second input shaft with the first input shaft and clutch means is provided for selectively engaging the second input shaft with the first input shaft through the gear means. The gear means and clutch are also housed within the extended portion of the housing. Such an axle drive arrangement has substantially greater size and weight than a drive axle utilizing a single input shaft. Moreover, tooth loads on the pinion gear as well as tooth loads on the gears interconnecting the first and second input shafts introduce off axis forces that tend to urge the input shaft from its proper axial alignment. Thus, the additional stresses exerted upon the bearings supporting the input shaft preclude reduction of the longitudinal spacing between the bearings supporting the input shaft.